Stop using reload_module

[Tim Burke]

We only use it in tests, but it can still cause headaches. For example, https://review.openstack.org/#/c/506002/ had some test failures that included output like

    First differing element 0:
    ShardRange<1a to 1z as of 0000000001.00000>
    ShardRange<1a to 1z as of 0000000001.00000>

which was strange since ShardRange.__eq__ is just

    if not isinstance(other, ShardRange):
        return False
    return self.lower == other.lower and self.upper == other.upper

Turned out, neither self nor other was actually an instance of ShardRange! ShardRange's id changed as a result of the reload.

https://review.openstack.org/#/c/506410/ gets us out of that particular hole, but reload_module is still being used in test_db_replicator and test_manager -- we should clean them up, as well.